In this post, you’ll learn more about the Oracle ErrorTNS-12521: TNS:listener does not currently know of instance requested in connect descriptor with the details on why you receive this error and the possible solution to fix it.
Oracle Error Description
TNS-12521: TNS:listener does not currently know of instance requested in connect descriptor
Reason for the Error TNS-12521: TNS:listener does not currently know of instance requested in connect descriptor
Cause: The listener received a request to establish a connection to a database or other service. The connect descriptor received by the listener specified in addition to the service name an instance name for an instance (usually a database instance) that either has not yet dynamically registered with the listener or has not been statically configured for the listener. This may be a temporary condition such as after the listener has started, but before the database instance has registered with the listener.
How to fix the Error TNS-12521: TNS:listener does not currently know of instance requested in connect descriptor ?
You can fix this error in Oracle by following the below steps
Action:
– Wait a moment and try to connect a second time.
– Check which instances are currently known by the listener by executing: lsnrctl services – Check that the INSTANCE_NAME parameter in the connect descriptor specifies an instance name known by the listener. – Check for an event in the listener.log file.